Merge pull request #943 from maccoda/raii_467

Adding destructor.

Author: steveklabnik

src/scope/raii.md

@@ -2,10 +2,10 @@
 
 Variables in Rust do more than just hold data in the stack: they also *own*
 resources, e.g. `Box<T>` owns memory in the heap. Rust enforces [RAII][raii]
-(Resource Acquisition Is Initialization), so whenever an object goes out of 
-scope, its destructor is called and its owned resources are freed. 
+(Resource Acquisition Is Initialization), so whenever an object goes out of
+scope, its destructor is called and its owned resources are freed.
 
-This behavior shields against *resource leak* bugs, so you'll never have to 
+This behavior shields against *resource leak* bugs, so you'll never have to
 manually free memory or worry about memory leaks again! Here's a quick showcase:
 
 ```rust,editable
@@ -61,10 +61,36 @@ $ rustc raii.rs && valgrind ./raii
 
 No leaks here!
 
+## Destructor
+
+The notion of a destructor in Rust is provided through the [`Drop`] trait. The
+destructor is called when the resource goes out of scope. This trait is not
+required to be implemented for every type, only implement it for your type if
+you require its own destructor logic.
+
+Run the below example to see how the [`Drop`] trait works. When the variable in
+the `main` function goes out of scope the custom destructor wil be invoked.
+
+```rust,editable
+struct ToDrop;
+
+impl Drop for ToDrop {
+    fn drop(&mut self) {
+        println!("ToDrop is being dropped");
+    }
+}
+
+fn main() {
+    let x = ToDrop;
+    println!("Made a ToDrop!");
+}
+```
+
 ### See also:
 
 [Box][box]
 
 [raii]: https://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization
 [box]: /std/box.html
-[valgrind]: http://valgrind.org/info/
+[valgrind]: http://valgrind.org/info/
+[`Drop`]: https://doc.rust-lang.org/std/ops/trait.Drop.html